Biofilm is otherwise called “biological film” or “slime”, and generally denotes a structure composed of high-molecular materials (e.g., polysaccharides and proteins) produced by microorganisms which adhere to the surface of a substance and proliferate in an aqueous system. The formation of biofilm entails a dangerous consequence attributable to microorganisms, thereby giving rise to many problems in various industrial fields. For example, when formed at the inside area of a pipe to be used in a food plant, biofilms easily peel off from the inside area and foreign materials intrude into a product, and also cause a food poisoning due to toxins emanated from microorganism. Furthermore, formation of biofilms on the metallic surfaces causes metal corrosion, thus accelerating the aging of facilities.
Furthermore, most of the microorganisms responsible for the formation of a biofilm tend to spoil the efficacy imparted by a microorganisms-controlling agent (e.g., bactericides and bacteriostatic agents), compared with microorganisms that are in a dispersed or suspended state in an aqueous system. In the medical field, there have been many reports revealing that microorganisms sneak into the narrow gaps or holes of a medical instrument (e.g., endoscope) and stay therein to form biofilms, leading to in-hospital infection. It is also well known that a biofilm formed on the teeth in the human oral cavity, the so-called dental plaque, is causative of dental caries or periodontal diseases, and these problems have long been studied.
So far, the idea of not proliferating microorganisms, particularly bacteria, by subjecting the bacteria to a bactericidal action or a bacteriostatic action has been studied as a way to prevent hazards attributable to biofilms. Patent Document 1 describes an antibacterial preparation in which arginine or a derivative thereof such as arginine hydrochloride, arginine ethyl ester or arginine-glutamic acid, is mixed with a compound exhibiting antibacterial activity. However, its effects are far from satisfactory, and this document rather shows antibacterial effects against microbial aggregates, not intended for the removal of biofilms.
In order to remove biofilms, a method of using a bactericide, a method of using a chelating agent, a method of using an enzyme and the like have been attempted. Patent Document 2 discloses a method of using a hypochlorite, an alkali metal hydroxide and a surfactant in combination. However, none of these methods are sufficient to effectively remove biofilms. As such, these methods still have grave problems.
That is, in the case of using a highly bactericidal cationic surfactant or a highly bactericidal agent having a feature of rapid-acting property, such as hypochlorite, the bactericidal property is rapidly lost due to the organic substances in the system or in the biofilms. Therefore, it is difficult for these agents to maintain the bacterial count reducing effect for a long time, and when the bactericidal effect disappears, bacteria start to proliferate again. In addition, since a bactericidal agent is not intended to remove biofilms, this agent is required to start its action before microorganisms attach to a surface and form a biofilm.
As discussed above, since biofilms are formed from various substances such as fungous forms, polysaccharides and proteins, it is difficult to completely remove biofilms by decomposing merely a part of these compounds. Therefore, while a method of removing biofilms by using an enzyme as disclosed in Patent Document 3 is effective to a certain extent, it remains difficult to completely remove biofilms, and this method does not have a suppressive action on biofilms, either. Thus the bacteria that have been left behind in biofilms are liable to proliferate again, so it is inevitable for macromolecular substances such as polysaccharides or proteins to be produced.
Biofilms tend to be formed in a humidified atmosphere, such as bathroom, cooking room, kitchen, toilet bowl, drainage ditch, drain pipe and medical instrument, where microorganisms can easily proliferate. But the types of contaminants differ from one place to another. For example, most of the contaminants frequently seen in the kitchen are oils and fats, while most of the contaminants frequently seen in the bathroom are metallic soaps, particularly calcium salts of fatty acids. Meanwhile, most of the contaminants liable to adhere to in the inner side of a toilet bowl are inorganic contaminants, while most of the contaminants liable to adhere to a medical instrument are protein contaminants, such as blood and body fluid. Biofilms coexist with such contaminants to form a complex of contaminants. Therefore, a technique that is capable of removing such a complex has been sought.    Patent Document 1: JP-A-08-151324    Patent Document 2: JP-A-2005-75873    Patent Document 3: JP-A-2001-508677